1. Field of the Invention
The present invention relates to a optical fiber connector for removably coupling an optical converter at the end surface of optical guide path provided for optical coupling between an optical fiber and an optical conversion element such as LED, phototransistor, photodiode, etc. and between optical fiber cables and more specifically to a connector which can stabilize the coupling efficiency by maintaining the coupling gap between materials to be coupled with a high accuracy.
2. Description of the Prior Art
An optical data transmission system utilizing optical fibers and optical convertion elements is now widely introduced into the field of communication systems and particularly the optical fibers are much expected for the future as a means of low loss and large capacity data transmission line.
An optical data transmission system is required to use connectors for coupling optical fiber and optical conversion element or end surfaces of optical guide paths of optical fibers.
For the coupling of them, a constant gap (for example, about 50 .mu.m) must be prepared between end surfaces of optical converters provided at the end part of optical guide paths.
Here, a prior art for coupling the optical guide paths of an optical conversion element and an optical fiber is explained with respect to FIG. 12 and FIG. 13. A light receptacle 1 comprises an optical conversion element 2 such as a LED, phototransistor, photodiode, etc. and is also provided with a cylindrical part 1b having the external thread 1a. At the center of end surface of optical guide path of such optical conversion element 2 is provided with an optical converter 2a which is a light receptor and emitter (consisting of receptor and emitter).
Meanwhile, a plug to be coupled with a light receptacle 1 is composed of a holding member which holds an optical fiber 4 and a cap nut having an engaging part 6a at the internal circumference thereof. This holding member 5 continuously forms a front cylindrical part 5a, a collar part 5b and a rear cylindrical part 5c. The front cylindrical part 5a holds an optical fiber 4, and both end surfaces of front cylindrical part 5a and optical fiber 4 are ground to the same surface level. The rear cylindrical part 5c holds an optical fiber cable 7 covering an optical fiber 4 and the optical fiber cable 7 is fixed in such a fashion that a fixing device 8 is engaged with the rear cylindrical part 5c which is also formed with a slit 5d.
The plug 3 can be coupled with such light receptacle 1 in this way. Namely, the front cylindrical part 5a of holding member 5 is inserted into a cylindrical part 1b and the cap nut 6 is engaged and both end surfaces of collar part 5b engages with the cylindrical part 1b and the engaging part 6a of cap nut 6. In this timing, the receptacle and plug are couplied in the condition shown in FIG. 12, forming a gap A between the optical converter of optical fiber 4 and the optical converter of light receptacle.
However, according to the prior art, the gap A between the optical converter 2a of optical conversion element 2 and the end surface of optical guide path of optical fiber 4 is determined by the length D of the front cylindrical part 5a of holding member and positional relation between the position where the collar part 5b collides with the end surface of cylindrical part 1b of light receptacle 1 and the optical converter 2a of optical conversion element 2.
Therefore, the gap A includes fluctuation of the length B from the internal rear wall 1c of light receptacle 1 to the cylindrical part 1b, the length C from the rear surface of optical conversion element 2 to the optical converter 2a and the length D from the end surface of holding member 5 to the collar part 5b, and the gap A exceeds the desired allowance of size and can no longer maintain the constant size. After all, the end surfaces of optical guide paths of optical converter 2a and optical fiber 4 are finally in contact with each other or separated too much.
As described above, when the end surfaces of optical guide paths of optical converter 2a and optical fiber 4 are in contact with each other, flaws may be generated at the contact surface or dewing phenomenon is generated by water, remarkably making unstable the optical signal transmission characteristic. Moreover, if the gap A is too large, the conversion efficiency in the optical signal transmission characteristic of receptacle and plug is lowered and transmission intensity of optical signal is deteriorated.